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 Post subject: Tesuji problem.
Post #1 Posted: Thu Aug 22, 2019 9:23 am 
Lives with ko

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So I'm currently going through the Segoe Tesuji dictionary and today encountered a slight issue where the proposed answer for one of the problem didn't help refute a line I had considered problematic (and which had led me to choose a more banal answer for the problem).

After thinking about it, I can't really find a way to prevent black from getting a ko, and so I'm getting unsure about whether my reading is wrong (and I missed something) or my judgement is (that ko might be perfectly fine for white). This is the problem :

Click Here To Show Diagram Code
[go]$$W White to play
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . X X . . . . . . . . . . . . . . . . |
$$ | . X O O . . . . . . . . . . . . . . . |
$$ | . O X O . . . . . . . . . . . . O . . |
$$ | . . X O . . . . . , . . . . X , . . . |
$$ | . . . X O . . . O . X . . . . X . . . |
$$ | . . X . O . . . . . . . . . . . . . . |
$$ | . . a . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]


The simple easy move is "a", since black can't cut that stone.

Click Here To Show Diagram Code
[go]$$W Simple way.
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . X X . . . . . . . . . . . . . . . . |
$$ | . X O O . . . . . . . . . . . . . . . |
$$ | . O X O . . . . . . . . . . . . O . . |
$$ | . . X O . . . . . , . . . . X , . . . |
$$ | . . 4 X O . . . O . X . . . . X . . . |
$$ | . 2 X 3 O . . . . . . . . . . . . . . |
$$ | . 6 1 5 . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]


(It might not be optimal but it makes for a good baseline). The tesuji is :w1: in the following diagram. If :b4: right to :w3:, then :w5: connect and then capture :b4:.

Click Here To Show Diagram Code
[go]$$W Main line according to the solution given
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . X X . . . . . . . . . . . . . . . . |
$$ | . X O O . . . . . . . . . . . . . . . |
$$ | . O X O . . . . . . . . . . . . O . . |
$$ | . 4 X O . . . . . , . . . . X , . . . |
$$ | . . 2 X O . . . O . X . . . . X . . . |
$$ | . 1 X 5 O . . . . . . . . . . . . . . |
$$ | . . 3 . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]


The issue I have is when black answer with another :b2:. Then the best line I can find is the following one :

Click Here To Show Diagram Code
[go]$$W :w9: at :w3:
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . X X . . . . . . . . . . . . . . . . |
$$ | . X O O . . . . . . . . . . . . . . . |
$$ | . O X O . . . . . . . . . . . . O . . |
$$ | . 8 X O . . . . . , . . . . X , . . . |
$$ | . 2 7 X O . . . O . X . . . . X . . . |
$$ | . 1 X 5 O . . . . . . . . . . . . . . |
$$ | . 6 3 4 . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]


:b8: might fight the ko at 7.

It's possible that this ko is a good enough result. If white lose, it's only a couple points less than the "standard" variation and since black does risk a fair amount he will probably get compensation elsewhere. But, since the loss of the ko isn't disastrous for black compared to simply connecting with :b2:, it might be better to fight the ko. So either the mainline isn't the best play by black, or I'm missing a way for white to unconditionally get as much profit.

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 Post subject: Re: Tesuji problem.
Post #2 Posted: Thu Aug 29, 2019 6:56 am 
Dies in gote

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Just a kyu here. But I think if white wins the ko, he will have extra 7 or 8 points compared to the tesuji variation, or 13 or 14 points compared to easy variation. Not only that, white will have secured two eyes, making the white group very strong, while the tesuji sequence will still leave white without any secured eyes, leaving some aji for black to exploit for future profit.
Hence, I think the soild connection of black at the tesuji sequence is honte, or the proper move, for black.

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 Post subject: Re: Tesuji problem.
Post #3 Posted: Thu Aug 29, 2019 7:14 am 
Gosei
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I would expect:


Click Here To Show Diagram Code
[go]$$W
$$ | . . . , . . . . . ,
$$ | . . . . . . . . . .
$$ | . . X . . . . . . .
$$ | . X X . . . . . . .
$$ | . X O O . . . . . .
$$ | . O X O . . . . . .
$$ | . . X O . . . . . ,
$$ | . 2 . X O . . . . .
$$ | . 1 X 3 O . . . . .
$$ | . . . . . . . . . .
$$ +--------------------[/go]


Then if black connects:

Click Here To Show Diagram Code
[go]$$W
$$ | . . . , . . . . . ,
$$ | . . . . . . . . . .
$$ | . . X . . . . . . .
$$ | . X X . . . . . . .
$$ | . X O O . . . . . .
$$ | 8 O X O . . . . . .
$$ | . . X O . . . . . ,
$$ | . 2 4 X O . . . . .
$$ | 6 1 X 3 O . . . . .
$$ | . 7 5 . . . . . . .
$$ +--------------------[/go]


he ends with gote, as opposed to sente.

And if black tries to capture the stone in the corner:

Click Here To Show Diagram Code
[go]$$W
$$ | . . . , . . . . . ,
$$ | . . . . . . . . . .
$$ | . . X . . . . . . .
$$ | . X X . . . . . . .
$$ | . X O O . . . . . .
$$ | . O X O . . . . . .
$$ | . . X O . . . . . ,
$$ | . 2 5 C O . . . . .
$$ | 4 1 X 3 O . . . . .
$$ | . . . . . . . . . .
$$ +--------------------[/go]


then this ko is very hard for black.

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 Post subject: Re: Tesuji problem.
Post #4 Posted: Thu Aug 29, 2019 7:27 am 
Lives with ko

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This might be a better ko to fight for white, but I'm unsure about how to best handle the descent at :b4:

Click Here To Show Diagram Code
[go]$$W
$$ | . . . , . . . . . ,
$$ | . . . . . . . . . .
$$ | . . X . . . . . . .
$$ | . X X . . . . . . .
$$ | . X O O . . . . . .
$$ | . O X O . . . . . .
$$ | . 6 X O . . . . . ,
$$ | a 2 5 X O . . . . .
$$ | . 1 X 3 O . . . . .
$$ | . b 4 . . . . . . .
$$ +--------------------[/go]


Not sure whether :w7: should be at a or b.

Edit : The ko seems to be worth around 8-10 points, but it's a couple point worse than the "simple" variation if you lose the ko. Assuming white get full compensation from his ko threat, then he would be at maybe around 6 points more than that "simple" variation. So I guess it's certainly better than it unless you don't have the ko threats. And I think this end up more or less equal in point total compared to the solid connection variation.

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